Based on a few other threads in this forum regarding installing EBS on Vista, you may want to save yourself the frustration and just go the VM route. If you have 3GB on your machine, I also suggest allocating at least 2GB to your VM; it'll be a bit frustrating otherwise.
I think it was a change i made in the actual Rapidwiz.cmd file as a parameter, if you have a search through the forums here you can find a page that someone explains it a lot better :-) Unfortunately i can't find the link now, sorry.
Just to update on this, i've decided that Vista is definitely not going to happen for me. I have however decided to move over to Opensuse 11.0 and again although this isn't a support OS by Oracle to host applications it works fine at the moment. So as this is a private project not having support is not an issue, but at least i have my e-Business R12 up and running.